The present invention relates generally to yarns, fabrics and protective garments knitted of such yarns and, more particularly, to an improved yarn which may be knitted into an improved, more comfortable, more flexible protective garment such as a glove.
Prior to the present invention, technological developments of cut resistant yarns for protective garments have followed essentially a two-pronged approach. The first approach was in connection with the use of Kevlar, which is a Dupont trademark for an aramid fiber, with the Kevlar fiber to be used in yarns for protective garments. By way of example and not by way of limitation, aramid fibers have been used to form yarns, with the yarns thereafter knitted to make protective garments, including protective gloves, as exemplified by Byrnes U.S. Pat. No. 3,883,898. In addition to the aramid yarn, aramid fibers have been used in combination with other materials such as wire to form a protective garment, such as a protective glove, with an increased/or cut-resistance. Examples of this concept may be found in Byrnes U.S. Pat. No. 4,004,295 and Byrnes et al. U.S. Pat. No. 4,384,449. This latter-most Brynes patent describes a particular yarn configuration, namely, a four-piece yarn configuration including a core and a covering. The core is composed of two parallel strands, one wire and one aramid fiber, and the covering is composed of two strand spirally-wrapped around the core, one clockwise and one counterclockwise, both of aramid fiber. This approach was expanded upon in Bettcher U.S. Pat. No. 4,470,251 where the yarn is made up of five pieces; three parallel strands comprising the core, and two wrappings comprising the cover. The Bettcher patent generally describes the core as comprising two wires and one aramid fiber, and the two wrappings with the first, or inner wrapping, being a high-strength synthetic fiber such as aramid and an outer wrapping preferably comprising three strands of nylon. This Bettcher patent further describes yet another version of the yarn, namely, a seven piece yarn with generally the same core as the five piece yarn. The first wrapping (closest to the core) is preferably an aramid. The next outermost wrapping is also an aramid, the next outermost wrapping is a three strand nylon, and the outermost wrapping is a three strand nylon.
In our prior applications, we disclosed the use of extended-chain polyethylene, such as the fiber manufactured by Allied-Signal, Inc., under the trademark Spectra in combination with other fibers and wire and in various configurations, for the purpose of an improved cut resistant or slash resistant yarn and garment. We explained the use of extended use polyethylene as avoiding numerous limitations and problems which occurred with the use of aramid fiber, such as, but not limited to, the fact that the polyethylene fiber has a substantially greater tensile strength than the comparable aramid fiber, the fact that polyethylene fiber is resistant to ultraviolet light and does not result in undesirable color change, as contrasted to aramid fiber, that the polyethylene fiber has increased abrasion resistance comparable to aramid, has only two-thirds of the density, has greater chemical resistance, and is inert, non-absorptive, non-allergenic and stable.
Unfortunately, there are certain limitations when extended-chain polyethylene fibers are utilized in a yarn for a protective garment. One of the most substantial limitations is that the extended-chain polyethylene fiber has an extremely limited heat resistance and, thus, when gloves knitted of yarns using extended-chain polyethylene are utilized, for example, in the food industry, the extended chain polyethylene fibers can not withstand the high temperature used for laundering and drying the gloves.
We overcame some but not all of these problems in a composite wire-fiber yarn and glove knitted therefrom, in the configuration described in our aforementioned U.S. Pat. No. 4,777,789, which illustrates various configurations of yarn in FIGS. 1, 2 and 5, the yarn including both wire and fiber, and we described how fibers, other than aramid and extended-chain polyethylene, may be used.
However, in many industries it is not desirable to utilize yarns and protective garments such as gloves which contain wire. As previously indicated, the wire may break and injure the hand of the wearer. In addition, gloves or garments made of yarn which contains wire will be electrically conductive, which is unsuitable for certain purposes. Wire, of course, is also thermally conductive.
Thus the yarns containing wire and either extended-chain polyethylenes, or aramids, have numerous limitations.